Abstract : In this chapter we argue that designers who collaborate in the workplace in order to evaluate proposed solutions and make decisions about them can learn informally about the characteristics of solutions, but it is more difficult to learn informally about the decision process itself. We illustrate two types of pivotal moments for decision making. The first—a pivotal moment for choice—leads to choosing between two solutions that have already been proposed through mobilizing criteria in arguments. The second—a pivotal moment for emergence—allows for the emergence of a new solution, by arguing against a first solution. This type of argumentation leads to explicit learning concerning the performance of the solution (e.g., can it be constructed, is it ergonomic, etc.) as criteria are elements that characterize performance. Our analysis shows that employing certain criteria provokes a change in focus: designers abandon one solution in favor of evaluating another, either already on the table or completely new. However, because we identify these “pivotal moments” a posteriori and because it is our analysis that allows us to formalize this phenomenon, it is not obvious that designers understand the potential and the importance of such pivotal moments while they are in the midst of the decision process. Our next step is to combine our detailed interaction analysis with a macro-level study about communicating with designers about our results within their organizational context. Our goal is to explore how designers think our results could improve their decision process.